The policy was toxic for the Conservatives during the election and widely interpreted as a potential tax raid on core Conservative voters.

Speaking at a lunch with journalists in Westminster, Mr Gauke said: "If you look at what the triple lock does, it has a ratchet effect because pensions go up by the higher of inflation or earnings, and in some years it will be one, in some years it will be the other.

"But over a period of time, it will mean that a greater and greater share of GDP goes to paying the state pension, even without any increases in pensioner numbers because that's just the way it works.

"Do I think that in 10, 20, 30 years' time, we will still have a triple lock? I cannot see in all honesty how we can."

Asked if the Tories could in two years' time introduce manifesto pledges which were left out of the Queen's Speech, including abolishing the triple lock, Mr Gauke said: "We will reflect on those measures and we haven't ruled anything out."